Advanced preparation process! Why is the supercritical fluid foaming technology used to compact the foundation and platform?

Supercritical foaming is a process technology that uses supercritical carbon dioxide and nitrogen instead of organic foaming agents to foam at a certain pressure and temperature. As a physical foaming technology, supercritical foaming is one of the most effective methods for producing microporous plastics, and the pore size of the plastic produced is usually between 0.1-10 μ m. According to different processes, supercritical foaming can be divided into supercritical bead foaming process and supercritical sheet foaming process, among which supercritical bead foaming is further divided into extrusion foaming, kettle foaming, etc. In terms of foaming agents, supercritical foaming agents mainly consist of carbon dioxide and nitrogen. This is because carbon dioxide and nitrogen have stable properties, are environmentally friendly, inexpensive, and have mild reactions that are easy to control. Nowadays, with the promotion of the national dual carbon target, the required panels for construction and infrastructure are developing towards lightweight, green, and functional. As an important way to achieve lightweight polymer materials, foaming technology plays a crucial role. Supercritical fluid foaming polymer is a safe and green process technology, which meets the rapidly developing emerging industries and high-quality living needs with excellent insulation, mechanical properties, and low-carbon environmental protection characteristics. Its market prospects are quite promising.

 

Among them, Linde Company, as a gas company specializing in the production of foaming agents such as nitrogen and carbon dioxide, provides high-purity foaming nitrogen, carbon dioxide and related pressurization and stabilization solutions, flow control equipment, customized gas supply for physical foaming enterprises, and ensures the stability of customer gas supply and the reliability of product purity. The company's main product is PRESS ® The high-efficiency liquid carbon dioxide pressurization device, with multiple advantageous functions, is widely used in fields such as supercritical physical foaming, insulation materials, mattresses, shoe materials, kitchen sponges, etc; Reliable and continuous supply of high-pressure supercooled liquid carbon dioxide; Automatic shutdown, with no energy consumption during shutdown; Gas assisted drive, no power supply required; Quality flow automatically adapts to customer needs; Flexible backup design to achieve maximum availability; Carbon dioxide comes from standard vacuum insulated tanks; Independent single tube, lower installation cost than circular pipeline; Low noise level; Optional device for temperature regulation.

 

Image: High pressure kettle foaming process flow

 

Source: official account @ plastic library network/intrusion and deletion

 

The foam formed by high-pressure reactor will then be transported to the shoe material factory for preliminary cutting using a laser cutting machine to obtain a rough midsole. By using a customized roughing machine and relying on the grinding wheel on top for fine polishing, a basic and accurate three-dimensional shape can be obtained. Finally, the rubber sheet of the outsole is molded and placed underneath, compressed and heated, and softened and bonded together to obtain a complete midsole and outsole.

 

3) Injection molding+supercritical foaming+compression molding

 

This method, also known as embryo membrane foaming, is used for the nitrogen midsole of Lightstrike Pro and C202 GT. The structure of an injection molding machine is similar to that of an extruder. The raw materials are heated and softened, and like a syringe, they are injected into the midsole mold through holes for heating and molding. In the case of chemical foaming, the foaming agent mixed in the raw materials will decompose at high temperatures to produce gas, thereby carrying out foaming. But in supercritical foaming, there is no foaming agent in the injection molding step, so a cold embryo without foaming is obtained. Then, dozens of cold embryos are placed on a bracket at once and sent to an autoclave for foaming. Therefore, the injection molding foam and one-step Mucell foam molding here are different.

 

It should be noted that in the step of loading into the high-pressure reactor, there are two options: one is to expose the semi-finished product that has been injected and place it on a rack, which has a relatively large degree of freedom and requires precise calculation and control of the foaming ratio to ensure that the finished product size matches the design value and improve the yield rate; The second is to place the semi-finished product into the midsole mold. When foaming and expanding, it is limited by the mold to the size of the finished product. However, if the limitation is excessive, it will lead to excessive compression of the midsole and a decrease in elasticity.

 

Supercritical fluid foaming applied in the food industry

Supercritical CO2 can be selectively extracted for different molecules by adjusting temperature and pressure, and its aromatic components are not easily oxidized and destroyed. Thanks to this, the research and application of supercritical fluid technology in the extraction of effective ingredients of hops, the extraction of natural essence from fruits and vegetables, the extraction of animal and vegetable fats from animals and plants, the removal of caffeine from tea, the removal of cholesterol from milk fat and other aspects have made great progress.

 

As early as 1993, a seabuckthorn oil industrial extraction device was built in China, successfully filling the industrial gap of SFE technology. In 1996, Tsinghua University built a pilot plant for hop extract SFE, which increased the utilization rate of hops from 25% to around 90%. At present, many domestic enterprises have used supercritical technology to extract natural spices, oils, etc., which has the advantages of heavy metal removal, compatibility, quantifiability, and fast flavor release, and is very popular among consumers.

 

Figure: Interior view of the workshop of Jiangsu Yuesheng Factory Source: official account @ Plastic Vision Changzhou Jinwei Chemical Complete Equipment Co., Ltd. is a high-tech manufacturer dedicated to the research, development and manufacturing of plastic extrusion molding equipment. The company's products include complete sets of biodegradable plastic modification equipment, whose typical applications are alloy blending of fully degradable plastics such as PLA, PBAT, PBS, PPC, PCL, TPS and PHA, starch filling modification, bamboo and wood powder filling modification, mineral powder filling modification, etc. Figure: Complete set of equipment for modification of biodegradable plastics Source: official account @ Biodegradable Materials Research Institute/Tai'an Zenith Mechanical Equipment Co., Ltd. is a production enterprise specializing in research, development and manufacturing of high-pressure equipment. The main equipment includes various new material equipment such as supercritical foaming equipment and new powder material equipment. The SL1000 supercritical foaming equipment - mass production machine is its star product, mainly used for large-scale production in factories. The advantage of this equipment is that it can use nitrogen and carbon dioxide for foaming; The temperature uniformity can reach within ± 1.5 ℃; Its foamable materials include various polymer elastomers such as EVA, TPU, PE, TPEE, PP, ABS, PEBAX, etc., mainly used in the fields of supercritical nitrogen and carbon dioxide foaming of sports shoe materials, boards, sheets, and new materials. Currently, due to the excellent performance of supercritical foaming materials prepared by supercritical foaming technology, they are widely used in shoe materials, packaging, wind power, 5G communication and other fields. With the expansion of the application fields of supercritical foaming materials, the demand for supercritical foaming technology will continue to be released, and the market development prospects are broad. However, it should still be noted that due to the characteristics of clean and environmentally friendly, stable performance, and fine cell structure of supercritical foaming technology, it is more difficult in terms of formulation, equipment, and foaming agent compared to traditional chemical foaming technology. In the future, supercritical physical foaming is expected to serve as a platform technology that connects upstream high-performance materials with downstream application scenarios. The market space is vast and the development speed is promising.